OXYGEN
Units, Definitions and O2 Availability
Units
•Barometric Pressure (mmHg)
•760 mmHg = 1 atmosphere (atm) = 100 kPa
•Partial pressure=
Pgas a = Gasa X Ptotal
Gasmix
Usually given as a percentage
Calculate partial pressure of O2 at
Sea level
Pgas a = Gasa X Ptotal
Nitrogen
Gasmix
• Atmospheric pressure is 1 atm at
sea level
• O2 content ~ 21%
What’s in our air?
78.08%
Oxygen
20.95%
Water Vapor
0 to 4 %
Argon
0.93%
Carbon Dioxide
0.036%
Neon
0.0018%
Helium
0.0005%
Methane
0.00017%
Hydrogen
0.00005%
Nitrous Oxide
0.00003%
Ozone
0.00004%
The respiratory pigments…
Why are they important?
100X increase!
The respiratory pigments…
Why are they important?
100X increase!
Greatly increase O2
carrying capacity of
blood
Hemoglobin (Hb)
 4 heme units:
= 1 iron-porphyrin + 1 protein
“heme”
(1 Hb can carry 4
oxygen molecules)
“globin”
Hb binds oxygen reversibly…
Hb + O2
Hemoglobin
HbO2
Oxyhemoglobin
Why is reversible binding important?
• what happens when O2 concentration is high?
(@ respiratory surface)
• what happens when O2 concentration is low?
(@ systemic tissues)
O2-Hb dissociation curves:
% saturation
Describe activity of Hb at different PO2
% of Hb binding sites bound
PO2
O2-Hb dissociation curves:
% saturation
Describe activity of Hb at different PO2
% of Hb binding sites bound
PO2
O2-Hb dissociation curves:
% saturation
Describe activity of Hb at different PO2
@ systemic tissues
PO2
@ respiratory surface
O2-Hb dissociation curves:
% saturation
Describe activity of Hb at different PO2
@ systemic tissues
PO2
@ respiratory surface
“Affinity”- how tightly two molecules bind together
Hb and O2….
Do you want your hemoglobin to have really High or
really Low affinity for O2?
A trade-off*:
 Optimal loading of O2 at
respiratory surface
Vs.
 Optimal unloading of O2
at tissues
* Hemoglobin’s affinity for O2 determines which
of these is favored
O2-Hb dissociation curves:
P50 is a measure of O2 affinity
% saturation
100
= PO2 at which
pigment is 50%
saturated with
O2
80
60
40
P50
20
0
30
60
90
PO2 (mmHg)
There are many different
forms of hemoglobin
=The product of different selective pressures
(i.e., an example of adaptation)
based on differences in protein portion
Show different affinities for O2
O2-Hb dissociation curves:
P50 is a measure of O2 affinity
• Hb with a high affinity has a lower P50
% saturation
100
•Animals that have Hb with high affinity:
Hb is saturated when O2 concentrations
are relatively low
80
60
•b/c Hb will not release O2 unless O2
levels are very low
40
• this kind of Hb favors O2 uptake (loading)
P50
20
0
30
60
90
PO2 (mmHg)
O2-Hb dissociation curves:
P50 is a measure of O2 affinity
• Hb with a low affinity has a higher P50
% saturation
100
•Animals that have Hb with low affinity: Hb
is only saturated when O2 concentrations
are relatively high
80
60
•b/c Hb is more likely to “let go” of O2,
even if O2 levels are pretty high
40
• this kind of Hb favors O2 delivery
(offloading)
P50
20
0
30
60
90
PO2 (mmHg)
Animals native to high altitudes
% saturation
100
80
Bar-headed goose
60
40
P50
20
0
30
60
90
PO2 (mmHg)
Animals native to high altitudes
Favors O2 loading
% saturation
100
80
Bar-headed goose
60
Hb has higher
O2 affinity
40
P50
20
0
30
60
90
PO2 (mmHg)
One more respiratory pigment…
Myoglobin (Mb)
 essentially identical to Hb but
only 1 heme unit
 always in muscle cells
 very high O2 affinity
Comparing dissociation curves…
myoglobin
% saturation
100
hemoglobin
80
60
40
20
P50
P50
0
30
60
90
PO2 (mmHg)
What is the function of myoglobin?
 May serve as an O2 reserve or
store
Facilitates diffusion of O2 into
muscle
 Very common in animals that
live in periodically low O2
environments
What I want you to know about respiratory pigments…
•Draw Hb-O2 dissociation curve and explain why it has that
shape
•Define and locate P50 on a Hb-O2 dissociation curve
•Draw dissociation curve for Hb’s with different affinities and
give physiological and ecological relevance of difference in
affinity.
•Compare dissociation curves for Hb and myoglobin and
give physiological relevance.
DIVING PHYSIOLOGY
Diving Physiology- marine
mammals
• Cetaceans (whales, dolphins and
porpoise)
• Pinnipeds (seals, sea lion, walrus)
• Sirenia (manatee, dugong)
• Mustelidae (sea otter)
• Carnivora (Polar Bear)
Some diving records…
Northern Elephant Seal
1600 m!
Sperm Whale
2000 m!
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Southern Elephant Seal
2 hours!
Dr. Sylvia Earle
375 meters,
1230 ft
(with scuba gear)
Free Diving (no scuba tank)
“no limits” record = 171 m
(561.02 ft)
“unassisted constant ballast”
record = 65 m (213.25 ft)
How do diving mammals deal with hypoxia? -need to be
able to store O2 for use when holding breath.
Where can an organism “store” O2?
Lungs
Blood
Muscle
Major internal O2 stores: Lungs
• Big lungs?
- no…let lungs collapse!
- many deep divers exhale before diving (20 - 60% capacity)
Lung O2 stores vs. Blood O2 stores
Major internal O2 stores: Blood
Deep Divers have more blood for their body size than
non-divers
More blood holds more oxygen!
Major internal O2 stores: Blood
• Oxygen carrying capacity (Hb)
- more Hb per red blood cell (RBC)
- more RBC’s per ml blood (higher Hematocrit)
Weddell Seal
Harbor seal
Human
Comparing Total O2 Stores:
What about our favorite curve?… Hb-O2 dissociation
% saturation
Left shift or right shift?
Shallow
divers
that rely
more on
lungs
Deeper Divers that
rely more on blood

stores of O2
PO2

Why???
•Divers that rely on O2 stores in lungs need high
affinity Hb that will pull O2 into blood even when
the partial pressure of O2 left in lungs has gotten
really low.
•Divers that rely on blood stores of O2 need lower
affinity Hb that will allow O2 to move into tissues
even when partial pressure of O2 in blood is
really low.